1. Introduction

Georadar method is commonly used for engineering and archeology since 1980 [1]. The target of this method usually is to image shallow/near surface. The method promises to give a better resolution and accuracy specially to detect the fault system and other subsurface structures in detail. Georadar is based on electromagnetic wave which detects the contrast of dielectric properties of medium. Due to the high frequency, georadar is able to effectively identify the shallow objects with a high resolution.

The instrument of georadar is equipped with transmitter and receiver antennas which has the ability to transmit and receive electromagnetic wave into and from

**46**

*Earth Crust*

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[1] Wikipedia contributors. Deep sea. Wikipedia, the free encyclopedia. October 19, 2018, 19:17 UTC. Available from: https://en.wikipedia.org/w/index. php?title=Deep\_sea&oldid=864831273. investigations. Haiyang Xuebao.

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the earth at certain frequency ranges. Data are recorded as time series in two-way time (TWT) manner which after processing can be converted into depth domain by adding the velocity model during processing. Figure 1 shows the georadar instrument and example of recorded data.

Due to the ability of detecting shallow object with high resolution, georadar has been applied in many fields with various objectives. Georadar is able to distinguish two different objects based on different electrical properties; hence, georadar are commonly used in various field such as environment study, mining, ground water, ancient artifact, and others. Not only able to detect the electrical properties contrast of material, but also georadar is able to detect the subsurface structure like faults and folds. Hence, the application of georadar for detecting the subsurface structures and monitoring of active faults for mitigation purposes are promising, especially for unstable area in the urban/suburban area with high population where other active source is prohibited.

The exact location of an active fault in urban area is very important to be known for the mitigation purposes. Hence, the potential landslide due to the unstable structure of this area can be warned early to avoid serious hazard or disaster. Many techniques have been used to monitor the stability and mitigate the potential landslide in the area around the active fault which is across the urban area. Nondestructive geophysical methods such as electrical method and electromagnetic method are commonly selected for the investigation and evaluation of the subsurface structure this area. Geo-penetrating radar (GPR) or georadar method is also a common geophysical method that is applied to understand the bedding subsurface and structure in the high-risk area in such condition.

fault system in this area becomes more significant. This chapter discusses the example of GPR technique for detecting fault in urban area. The background theory of GPR, design survey, and data gathering, processing, and interpretation of GPR data are discussed and applied for detecting an active fault of Lembang fault in

Identification of Active Faults in Landslide-Prone Regions Using Ground-Penetrating Radar…

Active fault (Lembang fault) located from west to east part of Bandung.

DOI: http://dx.doi.org/10.5772/intechopen.85397

Georadar technique is developed based on electromagnetic wave propagation

The propagation of the electromagnetic wave is perpendicular to the electrical field (E) and magnetic field (H) and controlled by the velocity and attenuation of medium. The properties of medium are also related to the mineral composition and also water saturation of medium. The velocity of wave propagation in the medium depends on the velocity of electromagnetic wave in the vacuum (c = 0.3 m/ns), relative dielectric constant (εr), and relative magnetic permeability (μ<sup>r</sup> ¼ 1 for

where P ¼ σ=ωε is an absorption factor and σ is conductivity of medium,

ϖ ¼ 2πf, where f is frequency and ε ¼ εrε<sup>o</sup> is vacuum permittivity (8.854 � <sup>10</sup>�<sup>12</sup> F/m). For the material with low loss, P� 0, the velocity of

∂2 E

Vm <sup>¼</sup> <sup>c</sup><sup>=</sup> ð Þ <sup>ε</sup>rμr=<sup>2</sup> <sup>1</sup> <sup>þ</sup> <sup>P</sup><sup>2</sup> <sup>þ</sup> <sup>1</sup> <sup>1</sup>=<sup>2</sup> (2)

<sup>∂</sup>t<sup>2</sup> (1)

theory. In one dimension (1D), the propagation of electromagnetic wave in

∂2 E <sup>∂</sup>z<sup>2</sup> <sup>¼</sup> με

Bandung, Indonesia.

Figure 2.

2. Background theory

nonmagnetic material):

georadar is

49

2.1 Georadar wave propagation

z-direction is explained by Maxwell equation:

Lembang fault is an example for active fault across urban area with high population density in Bandung, Indonesia. In this area, there are not less than 8 million people leaving around the Lembang fault. The length of this fault itself is about 29 km from east to west part of Bandung [3] as illustrated in Figure 2. Because of the compression system in this area, it is predicted that a huge accumulated energy is concentrated in this fault and potentially can be released any time as an earthquake. The earthquake then is predicted also which leads to trigger the local landslide in this area.

Due to some reasons such as soil stability and environmental concern, techniques such as seismic refraction and seismic reflection that use dynamite explosion as a source, are not allowed. Hence the use of georadar technique for identifying

Figure 1. (a) Georadar instrument [2], (b) example of recorded subsurface data.

Identification of Active Faults in Landslide-Prone Regions Using Ground-Penetrating Radar… DOI: http://dx.doi.org/10.5772/intechopen.85397

Figure 2. Active fault (Lembang fault) located from west to east part of Bandung.

fault system in this area becomes more significant. This chapter discusses the example of GPR technique for detecting fault in urban area. The background theory of GPR, design survey, and data gathering, processing, and interpretation of GPR data are discussed and applied for detecting an active fault of Lembang fault in Bandung, Indonesia.
